1. Field of the Invention
The present invention relates to communication devices which carry out communication by connecting communication circuits in a mesh form.
2. Description of the Prior Art
FIG. 1 is a simplified diagram of a communication system in which conventional communication devices are connected. In the diagram, reference numerals 1 through 7 are communication devices, 41 through 48 are circuits which connect communication devices of this kind with each other and with communication devices not shown, 11 through 17 are control units which control transmission and reception of the communication devices 1 through 7 respectively, and 311 through 371 denote one transmitting-receiving unit or a plurality of transmitting-receiving units provided in the communication devices 1 through 7 respectively.
Next, the operation of the conventional communication devices will be described. The respective control units 11 through 17 drive the transmitting-receiving units 311 through 371 and settle set communication links with control units of the adjacent communication devices 1 through 7 connected via the circuits 41 through 48. This means, for example, that when the communication device 1 communicates with the communication device 2, the control unit 11 of the communication device 1 and the control unit 12 of the communication device 2 drive the transmitting-receiving unit 311 and the transmitting-receiving unit 323 respectively to settle set a link via the circuit 41. The same processes are performed among the adjacent other communication devices 1 through 7.
On the other hand, it is possible to communicate via circuits even between communication devices not directly connected with each other, that is, like for example, between the communication device 1 and the communication device 5. In this case, after the settlement of the link, if a packet, that is, a unit in which data is transmitted via circuits is additionally provided with a network address for identifying a destination communication device, the communication device which has received the packet decides whether the packet is directed to itself or to one of the other stations in accordance with a destination network address in the packet, and at the same time, carries out routing processing which decides if the packet is directed to the other stations, to which circuit it should be transferred. In order that the communication devices 1 through 7 each may execute the routing processing, they store a route table for guiding a packet to adjacent communication devices (or its own station) from the destination network address.
In the above-mentioned conventional device, there was a problem that because the transmitting-receiving units 311 through 371 for each circuit are needed, control algorithms by which the control units 11 through 17 of the communication devices 1 through 7 control the respective transmitting-receiving units 311 through 371 are complex and moreover, the communication devices 1 through 7 become expensive.
In addition, there was a problem that the communication devices 1 through 7 each store a route table for the routing processing. But, in the case where alterations in the network structure such as additions, removals, and the like of the communication devices occurred, the route table had to be altered for all the communication devices, and in the case where the communication devices were installed in a wide area, trouble in renewal of the route table not only became profound but also it was generally difficult to make-up the route table without contradiction.